1. Technical Field
The present invention relates to an electrophoretic display sheet, an electrophoretic display device and an electronic apparatus, and more specially relates to an electrophoretic display sheet, an electrophoretic display device provided with the electrophoretic display sheet and an electronic apparatus provided with the electrophoretic display device.
2. Related Art
It is generally known that, if electric fields are allowed to act on a dispersion system in which fine particles are dispersed in liquid, the fine particles move (or migrate) in the liquid by the Coulomb force. This phenomenon is referred to as electrophoresis. In recent years, an electrophoretic display device that displays desired information (images) using the electrophoresis draws attention as a new display device.
The electrophoretic display device is characterized by exhibiting display memory characteristics and broad viewing angle characteristics even at the time of stoppage of voltage application and by possessing a capability of performing high contrast display with reduced electricity consumption.
The electrophoretic display device is a reflection type display that uses natural light as a light source. In order to realize high visibility, the electrophoretic display device is required to employ a transmission part of high transparency, a reflection part of high reflectance and an absorption part of high absorbency.
As a conventional electrophoretic display device, JP-A-2007-58151 discloses an electrophoretic display device manufactured by forming a microcapsule-containing layer containing a plurality of microcapsules and a binder on a first substrate, placing a second substrate on the microcapsule-containing layer and then applying heat and pressure thereto from above and below to bond the first substrate, the second substrate and the microcapsule-containing layer together.
In this regard, the microcapsules are produced by encapsulating an electrophoretic dispersion liquid, in which electrophoretic particles are dispersed, into a wall material (shell). Conventionally, a relatively flexible material, e.g., a composite material of gum arabic and gelatin, is frequently used as a constituent material of the shell.
In the case where the shell is composed of the flexible material, the microcapsules are compressed and deformed upon heating and pressurizing the microcapsule-containing layer. Therefore, the microcapsule-containing layer thus formed has a structure in which the respective microcapsules are crushed in an up-and-down direction (namely, a stone-wall structure).
In general, the flexible material is low in density. For this reason, if the shell is made of only the flexible material, the microcapsules suffer from insufficiency in pressure resistance (that is, a property with which the microcapsules resist the pressure applied thereto without being crushed) and in bleed resistance (that is, a property with which the dispersion liquid encapsulated into the microcapsules is kept against dissipation).
Consequently, it is highly likely that the microcapsules are damaged or the electrophoretic dispersion liquid is leaked out due to pressure applied when bonding the microcapsule-containing layer and the substrates together or due to an impact and a pressing force applied while the microcapsules are used and stored as a display device. This makes it difficult to stably operate the electrophoretic display device for a long period of time.